1. Field of the Invention
The present invention relates to wireless communication and more particularly, a method and an apparatus for providing feedback of channel state information.
2. Related Art
Machine-to-Machine (M2M) systems are getting attention as the next-generation communication technology. The IEEE 802.11 WLAN working group is pursuing development of a new standard to support the M2M systems. An M2M system refers to a network enabling exchange of information among machines with no human involved. Temperature sensor, humidity sensor, camera, consumer product such as TV, manufacturing machine in a factory, and even large-sized machine such as an automobiles can be counted as one element of the M2M system. With the advent of communication services such as smart grid, e-Health, and ubiquitous communication, M2M technology is becoming more accepted to support such services. A few important features of the M2M system can be summarized as follows.
1) Large number of stations: different from existing networks, the M2M technology assumes a large number of stations. This is so because the M2M technology inherently takes into account all of the possible sensors installed at home and office as well as the machines owned by individuals. Therefore, a considerable number of stations can be connected to a single Access Point (AP).
2) Low traffic load per station: since an M2M device has a traffic pattern of gathering and reporting information of the surroundings, frequent transmission of information is not necessary and the amount of information transmitted is relatively small.
3) Uplink-oriented: in most cases, M2M devices are so structured that they receive a command via downlink transmission, carry out the corresponding actions, and report the resulting data via uplink transmission. Since most of data are delivered through uplink transmission, uplink transmission becomes a primary means for M2M communication.
4) Station's long life expectancy: M2M devices are usually battery-powered and therefore, it is not easy for a user to charge them frequently. In this regard, any M2M device is required to guarantee a long life expectancy by minimizing battery consumption.
5) Automatic recovery function: since direct operation of M2M devices may not be accessible for humans in some cases, automatic recovery is necessary.